The objective of this project is to develop and validate a system for detection of induced base-pair substitutions and null mutations in single cells that has direct correlation to induction of known transmissible mutations in the biochemical specific locus test system. Specific antibodies to a somatic variant of MOD-1 induced by n-ethyl-n-nitrosourea will be produced from homozygous mice carrying the mutation. The specific marker will then be used to detect the induction of corresponding mutations in single sperm or somatic cells. Mutation frequencies will be directly compared between the transmissible germinal system and single cell system.